Calculating to mass of a water column above a specific point

[Emily Chetner]

Part D. I looked up the answer and input it already, which is why it says correct, but i am beyond stumped. No idea how to do this. I know the pressure at the dotted lines are equal and that pressure=force/area. I also know the pressure at an area is equal to whatever is above it so the pressure on the left arm= 1atmosphere but I am not sure if i would also include the 1kg weight. And I also know the pressure on the right arm is 1atm+ d*g*h and maybe + the kg weight. But I am so stumped on where to go from here

 

[haruspex]

I also know the pressure at an area is equal to whatever is above it so the pressure on the left arm= 1atmosphere but I am not sure if i would also include the 1kg weight. And I also know the pressure on the right arm is 1atm+ d*g*h and maybe + the kg weight.

Yes, you must include all the forces acting on the cap. Do that for both sides and you will get there.
(How did you get the right answer for the first part?)

 

[Emily Chetner]

Yes, you must include all the forces acting on the cap. Do that for both sides and you will get there.
(How did you get the right answer for the first part?)

i don't understand how to do this though. How do you add 1atmosphere to the 1kg weight?

 

[haruspex]

i don't understand how to do this though. How do you add 1atmosphere to the 1kg weight?

1 atm is a pressure, 1kg is a mass. What force on the cap results from each?

 

[Emily Chetner]

i honestly have no idea. I've been working on this for at least an hour and have made no progress. If I am supposed to incorporate all forces acting on this cap i don't get how to go that if I am dealing with mass and pressure?

 

[haruspex]

i honestly have no idea. I've been working on this for at least an hour and have made no progress. If I am supposed to incorporate all forces acting on this cap i don't get how to go that if I am dealing with mass and pressure?

1. What is the relationship between pressure and force? You must have been given an equation connecting them.

2. Why does placing a mass on top of something result in a force?

 

[Emily Chetner]

i have Pressure=Force/Area. But that hasnt done me any good this far because I literally have no idea how to do this problem. If i plug in numbers than I have 1atm=1kg/1pi and I have nothing to solve for so I don't know how to use this equation in this context

 

[haruspex]

i have Pressure=Force/Area. But that hasnt done me any good this far because I literally have no idea how to do this problem. If i plug in numbers than I have 1atm=1kg/1pi and I have nothing to solve for so I don't know how to use this equation in this context

It is a mistake to plug in numbers at the start. Always try to work symbolically. It makes the ideas clearer, and many other advantages.
You are not told the actual areas, but you are told the ratio between them. The trick is to create a variable, A say, for the smaller area, so the large area is 4A.
Let atmospheric pressure be P_a. Using your formula, what forces does the atmosphere exert on the two caps?

Please try to answer question 2 in my previous post.

 

[Emily Chetner]

ok, i give up, thanks though